Note 1 - Nature of Business and Significant Accounting Policies - Recent account developments (Details) - Pro Forma - Accounting Standards Update 2016-13 $ in Millions	Jan. 01, 2021 USD ($)
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in allowance for estimated losses on loans or leases	$ 1
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in allowance for estimated losses on loans or leases	$ 3